ISDN communications controller

ABSTRACT

A communications controller for interfacing multiple analog telephone terminals to an integrated services digital network (ISDN) line connected to a telecommunications network, the ISDN line having two bearer (B) channels and a data (D) channel. The controller comprises an ISDN interface providing a physical bi-directional interface to the two B-channels and the D-channel of the ISDN line. A base logic processor, and D-channel protocols process supports a Q.931 protocol with a central office of the telecommunications network and an X.25-based protocol with a remote device, via the ISDN interface and D-channel over which command and response packets to and from the base logic processor with the central office or the remote device are transmitted. Multiple analog interfaces are adapted to support respective telephone terminals for passing bi-directional analog voice signals. Selectable coders/decoders (CODECs), connected to respective analog interfaces, encode the analog voice signals to digital pulse code modulation (PCM) or adaptive differential PCM (ADPCM) and decode PCM or ADPCM to analog, as selected by the base logic processor. A bandwidth controller connects, via the ISDN interface, the encoded voice signals to or from the selectable CODECs with communication subchannels allocated among bandwidth of the B-channels, as directed by the base logic processor, forwarding precisely timed bandwidth availability. The communications controller supports up to five telephone connections concurrently through the telecommunications network.

This application is based on provisional application Ser. No. 60/013,174filed Mar. 12, 1996.

BACKGROUND OF THE INVENTION

This invention relates generally to digital communications systems and,in particular, to a system having a communications controller providingaccess to an integrated service digital network (ISDN).

Devices for interfacing multiple analog telephones to an ISDN line of atelecommunications network are known. For example, International PCTapplication WO 95/22218 published on Aug. 17, 1995 and U.S. Pat. No.5,305,312 issued on Apr. 19, 1994 disclose such devices. However, theseknown devices only support a maximum of two telephones in concurrentuse.

It is desirable to support more concurrently active telephones over thesingle ISDN line.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a new and improvedISDN communications controller.

The invention, therefore, according to a first aspect provides in asystem having a plurality of devices coupled to a first communicationscontroller which is connected to an integrated services digital network(ISDN) line of a telecommunications network through which a callconnection is established with a second communications controller, theISDN line having two bearer channels of predetermined bandwidth and adata channel, a method of interfacing the devices to the ISDN line forconcurrent communications over the call connection with the secondcontroller comprising the steps of: negotiating, on the data channel,between the first and second communications controllers appropriation ofone or more subchannels from the bandwidth of the two bearer channels;and allocating the one or more subchannels to respective devices of theplurality of devices.

In accordance with a second aspect, the invention provides An apparatusfor interfacing a plurality of analog telephone terminals to anintegrated services digital network (ISDN) line connected to atelecommunications network, the ISDN line having two bearer (B) channelsand a data (D) channel, the apparatus comprising: base logic; an ISDNinterface providing a physical bi-directional interface to the twoB-channels and the D-channel of the ISDN line; D-channel protocol meanssupporting communications with a central office of thetelecommunications network and with a remote device, via the ISDNinterface and D-channel over which command and response packets to andfrom the base logic with the central office or the remote device aretransmitted; a plurality of analog interfaces adapted to supportrespective telephone terminals for passing bi-directional analog voicesignals; a plurality of selectable coders/decoders (CODECs), connectedto respective analog interfaces, for encoding the analog voice signalsto digital pulse code modulation (PCM) or adaptive differential PCM(ADPCM) and decode PCM or ADPCM to analog, as selected by the baselogic; and bandwidth control adapted to connect, via the ISDN interface,the encoded voice signals to or from the selectable CODECs withcommunication subchannels allocated among bandwidth of the B-channels,as directed by the base logic, synchronized to the bit level betweencontrollers.

A home access network controller, manifesting the present invention, isa device that may interface subscriber premises telephone equipment witha public switched telephone network, through an ISDN interface. It isintended for residential or small office application, where it providescertain efficiencies and conveniences not previously available in thatsetting. A primary advantage is the capacity to support more than twoand up to five telephones in concurrent use.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the following descriptionof a home access network controller (HANC) system together withreference to the accompanying drawings, in which:

FIG. 1 is a schematic representing a first application of the HANCsystem;

FIG. 2 is a block diagram depicting functional elements of the HANC;

FIG. 3 illustrates an exemplary partitioning for the bandwidth of theISDN bearer channels;

FIG. 4 is a schematic representing a second application having a HANCand distributed internal line interface (DILI) to provide single linevoice distribution; and

FIG. 5 is a block diagram depicting functional elements of the HANC andDILI.

DETAILED DESCRIPTION

Referring to FIG. 1, for illustration of the present invention anapplication of the home access network controller (HANC) system isdiagrammed. Two HANC 10 communication controller devices are shown,labeled A and B respectively, which typically would be installed inseparate subscriber residences and interconnected through a backbonenetwork that provides many readily connectable full-duplex channels ofcommunications, namely a public switched telephone network (PSTN) 12.Each HANC 10 connects to the PSTN 12 via its own ISDN Basic RateInterface (BRI) line 14, consisting of two 64 Kbps bearer (B) channelsand one 16 Kbps data (D) channel multiplexed together on the sametwisted pair. Coupled to the HANC 10 at each subscriber residence aresubordinate devices, such as, one or more personal computers (PC) 16connected via an Ethernet local area network (LAN) 18, and up to fiveplain ordinary telephony service (POTS) telephones 20 connected in astar configuration via analog lines 22 which support dual tonemulti-frequency (DTMF) and switch-hook signaling with analog voice.Additional terminal device types (not shown) may be supported.

The HANC 10 represents the subscriber telephone equipment to the PSTN 12and functions as both a router and a dynamic bandwidth controller. Itaccepts calls announced on the BRI D-channel and routes them to the PC16 or the appropriate telephone 20, each of which may be identifiedexternally at the PSTN 12 by a unique directory number (DN). Converselyit delivers calls originating among its local subordinate devices, forexample, from a particular telephone 20 to a remote telephone 24 or fromthe PC 16 to an Internet Access Provider 26. The HANC 10 convertssignals to and from the lines 14, 22 between analog voice and either 64Kbps pulse code modulation (PCM) or 24 Kbps modified adaptivedifferential PCM (ADPCM) which supports an eight-to-three bitcompression, depending on whether the remote device to which it isconnected through the PSTN 12 is another HANC. It also acts as a networkgateway for PC protocols, encapsulating LAN packets for transmission onthe ISDN B-channels.

Referring to FIG. 2, the HANC 10 is characterized by various functionalelements which comprise an ISDN BRI interface 30, D-channels protocols32, bandwidth control 34, selectable coders/decoders (CODECs) 36, POTSinterfaces 38, Ethernet interface 40 and base logic 42.

The ISDN BRI interface 30 provides the physical bi-directional interfaceto the ISDN line 14 of the PSTN, and separates or combines the D-channeland two B-channels while deriving the line clock. It informs the baselogic 42 of line status.

The D-channel protocols 32 supports the physical and link layers for theQ.931 protocol with a central office of the PSTN and an X.25-basedprotocol with a remote HANC. Command and response packets are passed toand from the base logic 42.

The bandwidth control 34 connects digital voice to or from the CODECs 36with subchannels assigned among the 128 Kbps total bandwidth of theB-channels combined, as directed by the base logic 42. In other words,each B-channel supports a 64 Kbps transmission rate in the form of 8,0008-bit octets per second, and the bandwidth control 34 utilizes thecombined bandwidth of 128 Kbps to multiplex the digital voice by timedivision thereby creating communication subchannels in the B-channelbandwidth. Data derived from or destined to an attached PC can also bedirected to or from such a subchannel.

The selectable CODECs 36 encode analog voice signals to digital PCM orADPCM and decode PCM or ADPCM to analog, as selected by the base logic42. A CODEC 36 segregates the transmitted and received analog signals.It is the actual source (on its digital side) of the various signalingtones said to be issued on the POTS interface 38 below. There is oneCODEC 36, logically at least, for each subordinate telephone.

The POTS interface 38 supports the subordinate analog telephones, oneeach, providing the physical interface including DC current. It detectsswitch-hook transfer and DTMF tones, reporting both to the base logic42. As directed by the base logic 42, it issues dial tone, busy tone,remote ringing tone and local ringing AC and passes the bi-directionalvoice signal.

The Ethernet interface 40 connects the residential personal computer viaIEEE 802.3 physical and link protocols, providing packetized data to andfrom the base logic 42 at the rate of 10 Mbps.

The base logic 42 is the processing manager of the HANC. At power-on itoperates verification diagnostics, boots the operational software andseeks to establish connection with the PSTN central office on the BRID-Channel and with the PC. It communicates with the central office or aremote HANC via packets generated or examined on the D-channel. It makesthe bandwidth assignments executed by the bandwidth control 34 and mayexchange PC packets for transmission in or reception from a B-Channel.It understands call control sequences and directs the selectable CODECs36 and POTS interfaces 38 to execute them. It monitors the state of theHANC 10 device and attempts to recover from device failure by performingreset and restart. It keeps a status record accessible by the PC.

The HANC 10 and specifically the base logic 42 supports two categoriesof function in communication with an attached PC on the Ethernetinterface 40. It maintains a TCP socket by which PC software may exertcontrol and obtain status. It also passes PC packets through to thebandwidth control 34 for inclusion in the B-channels, and vice-versa,when the PC is connected on the public network.

According to a particular implementation, the base logic 42 may beeffected by a microprocessor operating under appropriate software, andthe bandwidth control 34 may be a set of shift registers. Alternatively,a digital signal processor (DSP) might be used in which case it couldintegrate several other functional elements. Low cost integratedcircuits are commercially available to support the CODEC 36 function andthe POTS interface 38, but for supporting only five telephone ports muchof that logic could be provided by the DSP. The Ethernet interface 40 isconventional functionality that may be implemented in separate hardware.However, with an aggregate signal bandwidth remaining of only 144 Kbps,or 6.9 microseconds per bit, or 116 DSP instructions per bit (60nanoseconds each), and no algorithmic challenge worse than a PCM/ADPCMlookup table, a single DSP may perform all HANC logic above the physicallayer.

Turning back to FIG. 1, in operation each HANC 10 may support at leasttwo concurrently active calls, for instance, with two of its subordinatetelephones 20 or one telephone 20 and the PC 16 connected externally,using the two B-channels on the BRI line 14 independently with eachseparately routed and connected. Alternately, if the only current useris the PC 16, both B-channels may be connected to the Internet AccessProvider 26 thereby delivering maximum bandwidth of 128 Kbps. For atelephone connection, the HANC 10 may convert between analog voice andthe PCM-encoded voice required on a B-channel, using 64 Kbps.

If the remote connection is another HANC 10, however, additionalconnectivity is available. In this case analog voice from the telephones20 is converted to 24 Kbps ADPCM before application to a B-channel. Whenboth B-channels are available between the two compatible HANCs 10, up tofive telephones 20, each using a three-bit allocation as a voicesubchannel, and the PC 16 using a one-bit allocation as a datasubchannel, may converse concurrently with their counterparts on the 16bits derived from the 8-bit octets of both B-channels combined.

In FIG. 3, illustrated is an exemplary partitioning of the B-channel8-bit octets to provide multiple communication subchannels whereby theup to five telephones and PC may communicate simultaneously over theISDN line. In the 8-bit octets of the first B-channel, bandwidth definedby bits 1-3 may be allocated as a voice subchannel which is labeled VS1and bits 4-6 as another voice subchannel VS2, in support of two separatetelephone calls. For a third active telephone call, the voice subchannelVS3 bandwidth may occupy bits 7-8 of the first B-channel and bit 1 ofthe second B-channel. A fourth and fifth telephone call may be allocatedvoice subchannels VS4 and VS5 which occupy bits 2-4 and 5-7,respectively, of the second B-channel bandwidth of which the remainingbit 8 may be employed as a data subchannel DS for PC communications.

If only one B-channel is available for HANC-to-HANC communications, forexample, because the other is busy with the remote telephone 24 shown inFIG. 1, two telephones 20 and the PCs 16 may converse concurrentlybetween HANCs. In this case, the 8 bit frame of the one B-channel forHANC-to-HANC communications may be partitioned into two three bit voicesubchannels and a two bit data channel. If the call is only between PCs16, all available bandwidth is allocated to that connection, else threebits for each ADPCM voice subchannel. The HANC 10, or HANCs 10-A and10-B in consultation, manage this bandwidth automatically in all cases.

The HANC 10 deallocates bandwidth when a call disconnects. It may alsodeallocate (i.e., deallocate and reallocate) when a new call originatesor arrives. In the case of two HANCs 10-A and 10-B originally connectingonly their PCs 16, a subsequent call between subordinate telephones 20requires deallocating three bits from the PC data subchannel toconstruct a new voice subchannel, but requiring consultation onlybetween HANCs. The more drastic case is a new call between a subordinateand an independent remote telephone, namely telephone 24. An entireB-channel must be deallocated from the HANCs 10 in this case anddiverted to serve the new call. This is accomplished by communication onthe D-channel between HANCs as well as the PSTN 12 central office. Inany case, if the necessary bandwidth is not available because too muchis already allocated to relatively inflexible voice traffic, the newcall is rejected on the D-channel or indicated busy to the subordinatetelephone 20.

When a first connection is established between a HANC (e.g., the HANC10-A) and a remote device through the PSTN 12, the HANC 10-A asks theremote if it is also a HANC using the X.25 protocol permitted end-to-endon the D-channel. If there is no valid response the HANC 10-A treats thenew call as POTS-to-POTS, but if a HANC identification is received(e.g., from the HANC 10-B), subsequent signaling between the two HANCs,10-A and 10-B, discloses the subsystem controlled by each as well as itscurrent state. At the end of this exchange, requiring at most a fewhundred milliseconds, each HANC 10-A and 10-B knows the devicesconnected to the other, their DNs, whether each is busy and how muchbandwidth is available for allocation.

The following describes in more detail particular processes forsubchannel bandwidth allocation and for external bandwidth extractionthat may be adapted to the HANC system of FIG. 1.

Once the connection exists via a channel through the PSTN 12 between thetwo HANCs 10-A and 10-B, the effect of subchannel bandwidth allocationis to permit complex data flow between the individual PCs, referenced as16-A and 16-B, simultaneously with multiple separate conversationsbetween telephone sets 20 on the two HANCs 10, without calling upon thePSTN 12 for assistance. The HANCs 10-A and 10-B accomplish this bycreating subchannels on the common network channel using time divisionmultiplexing. Subchannels exist only as demanded by the traffic andfunction by appropriating a part of the full bandwidth as negotiatedbetween the HANCs 10-A and 10-B. In the absence of demand for multiplesubchannels most of the bandwidth is allocated to the single user. Ifthat is a PC, its data are free to flow at the maximum rate.

Negotiation between HANCs 10 requires a subchannel reserved to suchspecial communication. This is assigned that minimum of the channelbandwidth appropriate to timely negotiation and is called the controlsubchannel.

The process of allocating and removing subchannels is initiated by enduser demand. An end user of one of the HANCs, such as the PC 16-A atHANC 10-A, first causes the initial connection through the PSTN 12 toanother terminator, such as HANC 10-B. HANC 10-A inquires via thecontrol subchannel whether that terminator is a compatible HANC. In theabsence of a positive response it permits the PC 16-A to communicate byits default protocol, if one exists, or breaks the connection withsuitable notification. If HANC 10-B responds, demonstratingcompatibility, the two controllers proceed to open the full channelbandwidth, less that of the minimal control subchannel, to communicationbetween the two PCs 16-A and 16-B. If the initial connection isrequested by an analog telephone set 20, such as 20-A1, the HANC 10-Astill elicits the compatibility indication. In its absence the “naturalbandwidth” required of ordinary voice communication, 64 Kbps PCM, isallocated and no suballocation on that B-channel is possible for theremainder of the call. If telephone set 20-A1 called a compatibletelephone, such as 20-B2, however, the HANCs 10-A and 10-B allocate the24 Kbps of bandwidth as required by the ADPCM voice encoding, with therest held in reserve for further demand.

Subchannel allocation employs the following steps, given the connectionalready established between PC 16-A and PC 16-B. As part of the initialcompatibility exchange, each HANC 10-A and 10-B informed the other ofthe identifiers, i.e., telephone numbers, and types of all attachedend-user devices.

1) User at telephone 20-B3 dials the DN of telephone 20-A2.

2) HANC 10-B notifies 10-A of this demand and proposes the extraction ofa specified part of the current PC bandwidth to support the telephoneconversation, using the control subchannel.

3) HANC 10-A investigates the state of telephone 20-A2, which may beidle, busy or non-working, and reports accordingly. If idle itinstigates ringing at that telephone while HANC 10-B reflects a ringingtone to telephone 20-B3.

4) If no user answers telephone 20-A2, the user at telephone 20-B3eventually abandons the call and HANC 10-B so notifies HANC 10-A.

5) If telephone 20-A2 answers, HANC 10-A ceases to ring and accedes tothe suballocation request. Coincident with an accession messagetransmitted on the control subchannel, HANC 10-A extracts sufficientbandwidth from the PC subchannel to form the specified voice subchannel.After a specified period upon or after the close of the accessionmessage, HANC 10-A effects the bandwidth changeover in its full channeltransmission toward HANC 10-B.

6) HANC 10-B transmits an acknowledgment on the control subchannel.After a specified period upon or after the close of the acknowledgmentmessage, HANC 10-B effects the bandwidth changeover in its transmissionstoward HANC 10-A. Note that by measuring from the close of the accessionand acknowledgment messages, synchronization of bandwidth changeover isobtained with bit-level timing accuracy. Also, the point in time whenthe bandwidth changeover is effected upon or after the close of theaccession and acknowledgment messages may be predetermined, whetherimmediate or after a fixed time period.

7) Voice communication proceeds on the new subchannel, using the ADPCMencoding method, simultaneously with data transfer on the PC subchannel.Additional voice subchannels may also be opened by the same process. Theonly effect apparent upon interPC communications is a reduction inthroughput, which may or may not be of concern.

8) The user at telephone 20-A2 hangs up.

9) HANC 10-A sends a deallocate message to HANC 10-B on the controlsubchannel, identifying the voice subchannel to be deallocated. After aspecified period upon or after the close of the deallocation message,HANC 10-A restores that amount of bandwidth to the PC subchannel andeffects the bandwidth changeover in its transmissions toward HANC 10-B.

10) HANC 10-B sends an acknowledgment message to HANC 10-A and likewisechanges over to the larger PC subchannel bandwidth after theacknowledgment is complete.

Part of the bandwidth used between two HANCs 10 may be extracted topermit communications with outside devices, such as, the independentanalog telephone 24. The process of extracting bandwidth is initiated byend user demand, either from outside the context of two connected HANCs10-A and 10-B, or from a dependent user of a particular HANC 10 whowishes to communicate with an outsider.

Bandwidth extraction can be performed even when the HANCs 10 are usedonly by attached telephones 20. The process is best illustrated,however, by its operation when the principle communication is betweenPCs 16.

As part of the initial compatibility exchange, each HANC 10 informed theother of the identifiers, i.e., telephone numbers, and types of allattached end-user devices.

Outsider initiated extraction involves the following steps:

1) User at telephone 24 dials the DN of the telephone 20-A2 connected toHANC 10-A.

2) The PSTN 12 notifies the HANC 10-A of the incoming call, usingprocesses equivalent to “Call Waiting” and “Caller-ID” as conventionallypracticed.

3) HANC 10-A examines its outstanding bandwidth allocation. If bandwidthinsufficient to support standard network voice remains unassigned orsuch bandwidth cannot be removed from PC support without disconnectingany conversation or exchange already in progress, it ignores or rejectsthe incoming call, according to the appropriate backbone networkprotocol.

4) If the necessary bandwidth can be found, however, HANC 10-A notifiesHANC 10-B of the demand, using the control subchannel, and proposes theextraction of a sufficient part of the current PC bandwidth to supportordinary voice.

5) HANC 10-B accedes to the extraction request. Coincident with anaccession message transmitted on the control subchannel, B extractssufficient bandwidth from the PC subchannel to form the specified voicesubchannel. After a specified period upon or after the close of theaccession message, HANC 10-B effects the bandwidth changeover in itsfull channel transmission toward HANC 10-A.

6) HANC 10-A transmits an acknowledgment on the control subchannel.After a specified period upon or after the close of the acknowledgmentmessage, HANC 10-A effects the bandwidth changeover in its transmissionstoward HANC 10-B. Note that by measuring from the close of the accessionand acknowledgment messages, synchronization of bandwidth changeover isobtained with bit-level timing accuracy.

7) HANC 10-A accepts the incoming call by notifying the PSTN 12 andcreates an internal path for communication between telephones 20-A2 and24.

8) Voice communication proceeds on the extracted channel, using thenetwork standard encoding method, simultaneously with data transferbetween HANCs 10 on the PC subchannel. Additional voice subchannels mayalso be opened between the HANCs 10, using a different process. The onlyeffect apparent upon interPC communications is a reduction inthroughput, which may or may not be of concern.

Insider initiated extraction involves the following steps:

1) The user at telephone 20-A2 dials a DN not administered by HANC 10-B,such as the number corresponding to telephone 24.

2) HANC 10-A examines its outstanding bandwidth allocation. If bandwidthinsufficient to support standard network voice remains unassigned orsuch bandwidth cannot be removed from PC support without disconnectingany conversation or exchange already in progress, it informs thetelephone 20-A2 user that local circuits are busy.

3) If sufficient bandwidth is found, however, HANC 10-A notifies HANC10-B of the demand, using the control subchannel, and proposes theextraction of a sufficient part of the current PC bandwidth to supportordinary voice.

4) HANC 10-B accedes to the extraction request. Coincident with theaccession message transmitted on the control subchannel, B extractssufficient bandwidth from the PC subchannel to form the specified voicesubchannel. After a specified period upon or after the close of theaccession message, HANC 10-B effects the bandwidth changeover in itsfull channel transmission toward HANC 10-A.

5) HANC 10-A transmits an acknowledgment on the control subchannel.After a specified period upon or after the close of the acknowledgmentmessage, HANC 10-A effects the bandwidth changeover in its transmissionstoward HANC 10-B.

6) HANC 10-A notifies the PSTN 12 of its call to the DN of telephone 24using an appropriate part of its full channel bandwidth and assigns thatportion to network control, permitting the user at telephone 20-A2 tohear the network call progress reports.

7) If the telephone 24 answers, voice communication between telephones20-A2 and 24 proceeds on the extracted channel, using the networkstandard encoding method, simultaneously with data transfer betweenHANCs 10 on the PC subchannel.

8) The user at telephone 20-A2 hangs up.

9) HANC 10-A notifies the PSTN 12 that the connection between telephones20-A2 and 24 no longer exists.

10) HANC 10-A sends a restore bandwidth message to HANC 10-B on thecontrol subchannel, identifying the voice subchannel to be restored foruse by the PCs 16. After a specified period upon or after the close ofthe restore message, HANC 10-A restores that amount of bandwidth to thePC subchannel and effects the bandwidth changeover in its transmissionstoward HANC 10-B.

11) HANC 10-B sends an acknowledgment message to HANC 10-A and likewisechanges over to the larger PC subchannel bandwidth after theacknowledgment is complete.

In application of the above processes for subchannel bandwidthallocation and bandwidth extraction to the HANC system, the ISDND-channel may be utilized for the control subchannel. If the initialconnection through the PSTN 12 is established between PCs 16, the calledHANC furnishes the DN of its second B-channel as part of thecompatibility exchange and the calling HANC immediately calls throughthe PSTN 12 on the second B-channel, thus obtaining the maximum 128 Kbpsfor use in passing PC data. Subsequent demands by telephones 20 to sharethe bandwidth are negotiated on the D-channel as previously described.

Connections through the PSTN 12 are obtained using the ISDN standardQ.931 protocols on the D-channel. The calling HANC sends a compatibilityinquiry via the end-user protocols on the D-channel, which are specifiedto agree with X.25 standards. If it receives the compatibility indicatoras an X.25 response, the call proceeds as described above.

Notifications by the PSTN switch of incoming calls, such as the onedescribed from telephone 24, arrive on the D-channel in the switchsupported protocol. Subsequent negotiations between HANCs 10 use X.25protocols. The extraction of bandwidth to support the voice demandproceeds as previously described. Here an entire 64 Kbps B-channel mustbe allocated to the external PCM voice flow. Only one such externalconnection can be supported simultaneously with the interHANCconnection, which uses the other B-channel. That B-channel can still besubdivided, however, among PCs 16 and telephones 20 attached to the twoHANCs 10-A and 10-B.

A further feature supported by the HANC 10 is a method for convenientcall acceptance. To obtain the convenience of answering a telephone callin any part of a residence, a traditional method would place extensiontelephones in every part where such convenience is desired. This methodbears the disadvantage that so long as an extension is busy, all theothers are unavailable for separate use.

When the convenient call feature is active on the HANC 10, it rings allits idle telephones 20 simultaneously with a distinctive ringingpattern, preassigned according to DN, upon receipt of a call intendedfor any one of the DNs. That is, at the switch in the PSTN 12, the ISDNline 14 of the HANC 10 is represented by six DNs, one for the PC 16 andone for each analog telephone 20. Each DN is identified by its ownpattern of long rings, short rings or variably spaced longs and shorts.The HANC 10 maintains the association between the DNs and correspondingdistinctive ring patterns, and it selects the appropriate pattern for anincoming call according to the dialed DN received over the data channelfrom the switch.

The first idle telephone seen by the HANC 10 to go off-hook is thenconnected to the incoming call. The other idle telephones remainavailable for another call, either outgoing or incoming, in which casethe same procedure is repeated. Furthermore, the same procedure ofcourse may be applied to incoming calls from another HANC. Describedabove is a process for connecting the incoming call to the telephonegone off-hook.

This method for convenient call acceptance is applicable to telephonesets 20 wired to the HANC 10 either in the star configuration shown inFIG. 1 or by a local voice distribution method, described in thefollowing.

The typical residential subscriber of telephone services uses a singletelephone line for distribution of the service within his residence.Though several telephone sets may be attached to that line, they alloperate interdependently as extensions and are represented by one DN atthe public switch.

FIG. 4 illustrates a variation in the HANC system that supports theattachment of up to five POTS telephones by a single telephone line, yetpermits each to converse independently of the others and to berepresented by its own DN at a central office of the PSTN. A HANC 50connects to the PSTN 52, via a national standard ISDN BRI line 54consisting of two 64 Kbps B-channels and a 16 Kbps (control) D-channel,multiplexed together on the external line 54. It supports the attachmentof a (i.e., one or more) PC 56 via 802.3 LAN 57. Up to five local analogtelephones 58 may be attached via respective distributed internal lineinterfaces (DILIs) 60 devices to the HANC 50 over a dual twisted pairdistribution line 62 located internal to a subscriber's residence.Additional device types may also be supported (not shown).

The HANC 50 interfaces with the public switch on the BRI D-channel andthus arranges connectibility through the PSTN 52. It is responsible fortransferring encoded voice between the ISDN B-channels and thedistribution line 62 to the DILIs 60 and for signaling the DILIs 60 toinform them of call progress. Each DILI 60 interfaces an analog POTSline 64 to the distribution line 62 from the HANC 30. It receives itsoperating power down that same line 62.

Referring to FIG. 5, illustrated are the functional elements of the HANC50 and the DILIs 60. The HANC 50 is similar to the HANC 10 embodiment inFIG. 2, except that the CODECs 36 and the POTS interfaces 38 are removedfrom the HANC 30 and now consigned to the DILIs 60, identified byreferences 36′ and 38′ respectively. In their place, the HANC 50receives a PCM converter 66. The digitally encoded voice signalsprovided by the bandwidth control 34, either in PCM or ADPCM form, aremade only PCM by the PCM converter 66 for transmission on thedistribution line 62 to the DILIs 60.

In each DILI 60, the CODEC 36′ converts analog voice to PCM voice andvice-versa passed between the POTS interface 38′ and a HANC interface68. The POTS interface 38′ provides an analog line connector, linetermination and impedance matching, pulse dial and DTMF detection, dialtone generator, busy tone generator, remote-ringing tone generator, anda ringing voltage generator. Functionality of the HANC interface 68includes a distribution line connector, DC power separation andpropagation on the distribution line 62, protocol support for callprogress communication with the HANC 50, distribution physical protocolsupport for frame detection and channel (i.e. time slot) identification,a configurator to assign distribution channels, and a bi-directionalframe redriver with drop-and-insert channel support. Each DILI 60 may beoptionally equipped with caller identification (ID) displaycapabilities.

The distribution line 62 from the HANC 50 is a double twisted pair,typical residence wiring, one pair for each direction. All DILIs 60 arepowered by DC on the combined pair. Signals are driven in a standarddigital manner, such as Manchester or NRZI encoding, capable of ACcoupling, at a bit rate relatively low but high enough to include fivedigital voice channels and five control channels in individual timeframes. Each frame consists of five time slots corresponding torespective DILIs 60, wherein each time slot includes one of the voicechannels and one of the control channels. The frame start is identifiedby recurrence of a fixed bit pattern. A control channel is used toinform the HANC 50 of the switch-hook status of a particular telephone58 and a dialed telephone numbers or DTMF tones detected. In the reversedirection it conveys instructions to issue ringing voltage, to issuedial tone, busy tone or ringing tone and to display a delivered callerID. In the inbound direction to the HANC 50, each DILI 60 uses adrop-and-insert technique, well known from T1 multiplexers, to insertits signals at the appropriate time slot.

Turning back to FIG. 4, the following illustrates the process to place acall from a DILI-connected telephone 58.

1) A user lifts receiver at a particular telephone 58.

2) The DILI 60 connected to that telephone 58 detects off-hook state andsignals the HANC 50 on that DILI's control channel.

3) The HANC 50 responds with an instruction for the DILI 60 to issuedial tone.

4) The DILI 60, responsive to the received instruction, generates dialtone to the receiver of the attached telephone 58.

5) The user keys a called DN in DTMF tones.

6) The DILI 60 detects these tones, and transmits numeric codes to theHANC 50 on the control channel.

7) On receipt of the first numeric code, the HANC 50 instructs the DILI60 to cease generation of the dial tone.

8) The HANC 50 requests connection to the called DN via itscommunications 54 with the central office of the PSTN 52. If the remotetelephone (i.e., called DN) is busy, the HANC 50 instructs the DILI 60to issue a busy tone. If the remote is being rung, the HANC 50 mayeither feed the remote ringing tones through to the DILI 60, if theswitch provides any, or instruct the DILI 60 to generate its own.

9) The DILI voice channels, inbound and outbound, are activated throughto the PSTN 52, with the DILI 60 performing basic analog to digitalcoding-decoding and the HANC 50 assuring compatibility with PSTN switchor remote HANC (if the called DN corresponds to such) requirements.

When a remote telephone calls the DN of a DILI-connected telephone, thefollowing process is effected.

1) The central office switch of the PSTN 52 notifies the HANC 50 of thecalled DN.

2) The HANC 50 determines the particular DILI 60 that owns this DN.

3) If the DILI 60 and the dependent telephone 58 are busy, the HANC 50so notifies the PSTN switch. Otherwise, via that DILI's control channel,the HANC 50 instructs the DILI 60 to generate ringing voltage and todisplay the caller ID.

4) A user lifts receiver at that telephone 58.

5) The DILI 60 informs the HANC 50 on the control channel that thetelephone 58 is off-hook.

6) The HANC 50 instructs the DILI 60 to end ringing voltage and toactivate its voice channels in both directions.

It is noted that the above processes are representative but notexhaustive.

If the local telephones 58 are connected to remote telephones notassociated with a remote HANC (not shown), only two of the telephones 58may be active simultaneously, one on each B-channel. If they aremediated by a remote HANC, however, in support of interfamilycommunications or small offices, up to five telephones 58 may be activeconcurrently, along with the PC 56. The method of interconnecting the upto five telephones through multiple HANCs was described above.

Those skilled in the art will recognize that various modifications andchanges could be made to the invention without departing from the spiritand scope thereof. It should therefore be understood that the claims arenot to be considered as being limited to the precise embodiment of thesystem set forth above, in the absence of specific limitations directedto each embodiment.

I claim:
 1. In a system having a plurality of devices coupled to a firstcommunications controller which is connected to an integrated servicesdigital network (ISDN) line of a telecommunications network throughwhich a call connection is established with a second communicationscontroller, the ISDN line having two bearer channels of predeterminedbandwidth and a data channel, a method of interfacing the devices to theISDN line for concurrent communications over the call connection withthe second controller, the method comprising: negotiating, on the datachannel, between the first and second communications controllersappropriation of one or more subchannels from the bandwidth of the twobearer channels; and allocating the one or more subchannels torespective devices of the plurality of devices, wherein the subchannelsare allocated bits from one or more of the bearer channels so as toallow at least five devices to be allocated different call connectionsfrom the two bearer channels, and wherein each of the devices therebyconnects through at least one of the two bearer channels to a differentdevice.
 2. A method as claimed in claim 1, wherein the step ofnegotiating the appropriation of a subchannel includes: one controllerof the first and second communication controllers sending a request forthe subchannel to the other controller, wherein the request specifiesbandwidth for the subchannel; the other controller transmitting anaccession message and, after a specific period upon close of theaccession message, effecting the bandwidth changeover in the fullchannel transmission of the other controller towards the one controller;and the one controller transmitting an acknowledgement message and,after the specific period upon close of the acknowledgement message,effecting the bandwidth changeover in the full channel transmission ofthe one controller towards the other controller.
 3. A method as claimedin claim 2, wherein the specific period is a predetermined time intervalfollowing the close of the accession message or the acknowledgementmessage.
 4. A method as claimed in claim 3, wherein the specific periodis immediately following the close of the accession message or theacknowledgement message.
 5. A method as claimed in claim 1, wherein theplurality of devices include telephones; and each subchannel allocatedto the individual telephones, as a voice subchannel, comprises 24 Kbpsbandwidth for a digital voice signal.
 6. A method as claimed in claim 5,wherein the digital voice signal is encoded in three bit adaptivedifferential pulse code modulation (ADPCM).
 7. A method as claimed inclaim 6, wherein the plurality of devices includes at least one dataprocessing device and the subchannel allocated to the at least one dataprocessing device, as a data subchannel, comprises available bandwidthof the two bearer channels not allocated to the telephones.
 8. A methodas claimed in claim 7, wherein the predetermined bandwidth of the twobearer channels is 128 Kbps, which supports a maximum of five 24 Kbpsvoice subchannels and a minimum of 8 Kbps for the data subchannel.
 9. Amethod as claimed in claim 8, wherein the telephones are analogtelephones and further comprising, for each analog telephone having beenallocated a voice subchannel: encoding an outgoing analog voice signalfrom the analog telephone into an outgoing ADPCM digital voice signalwhich is transmitted over the voice subchannel allocated thereto; anddecoding an incoming ADPCM signal received from that voice subchannelinto an incoming analog voice signal which is passed to the analogtelephone.
 10. A method as claimed in claim 1, further comprisingsharing the predetermined bandwidth of the two bearer channels with adata device and allocating the data device at least one bit, such thatthe data device shares the predetermined bandwidth with up to fivedifferent call connections.
 11. A method as claimed in claim 10, furthercomprising deallocating bandwidth that has been allocated to the datadevice and allocating it to a new call connection that is established.12. A method as claimed in claim 10, further comprising allocatingbandwidth from a terminated call connection to the data device toincrease the bandwidth allocated to the data device.
 13. A method asclaimed in claim 1, wherein allocating the one or more subchannels torespective devices of the plurality of devices comprises allocating atleast one bit from each of the two bearer channels to at least one ofthe respective devices, such that the at least one respective device isallocated bandwidth from both of the bearer channels.
 14. A method asclaimed in claim 1, wherein allocating the one or more subchannels torespective devices of the plurality of devices comprises allocatingthree bits, from one or more of the two bearer channels, to each of therespective devices.
 15. A method as claimed in claim 1, furthercomprising communicating between the first communications controller anda line interface unit using a frame format which comprises a separatecontrol channel and a separate data channel for each of the plurality ofdevices, wherein the line interface unit is disposed between theplurality of devices and the first communications controller.
 16. Anapparatus for interfacing a plurality of analog telephone terminals toan integrated services digital network (ISDN) line connected to atelecommunications network, the ISDN line having two bearer (B) channelsand a data (D) channel, the apparatus comprising: base logic; an ISDNinterface providing a physical bi-directional interface to the twoB-channels and the D-channel of the ISDN line; D-channel protocol meanssupporting communications with a central office of thetelecommunications network and with a remote device, via the ISDNinterface and D-channel over which command and response packets to andfrom the base logic with the central office or the remote device aretransmitted; a plurality of analog interfaces adapted to supportrespective telephone terminals for passing bi-directional analog voicesignals; a plurality of selectable coders/decoders (CODECs), connectedto respective analog interfaces, for encoding the analog voice signalsto digital pulse code modulation (PCM) or adaptive differential PCM(ADPCM) and decoding PCM or ADPCM to analog, as selected by the baselogic; and bandwidth control adapted to connect, via the ISDN interface,the encoded voice signals to or from the selectable CODECs withcommunication subchannels allocated among bandwidth of the B-channels,as directed by the base logic, synchronized to the bit level betweencontrollers, wherein the communication subchannels are allocated bitsfrom one or more of the B-channels, so as to allow at least five analogtelephone terminals to be allocated different call connections from thetwo B-channels, and wherein each of the analog telephone terminalsthereby connects through at least one of the two B-channels to adifferent device.
 17. An apparatus as claimed in claim 16, wherein theD-channel protocol means supports a Q.931 protocol by which theapparatus communicates with the central office.
 18. An apparatus asclaimed in claim 17, wherein the D-channel protocol means supports anX.25-based protocol by which the apparatus communicates with the remotedevice.